Requests a property to be delivered to you as a string, through your sink delegate.
If the value is null, it means the property could not be retreived. If valueIsJson, it should
be interpreted as json, otherwise, it is just a plain string.
The sink should always be called exactly once for each call (it is basically a return value, but it might
use a local buffer it maintains instead of allocating a return value).
Requests a property to be delivered to you as a string, through your sink delegate.
If the value is null, it means the property could not be retreived. If valueIsJson, it should be interpreted as json, otherwise, it is just a plain string.
The sink should always be called exactly once for each call (it is basically a return value, but it might use a local buffer it maintains instead of allocating a return value).